Carrier 48EJ, 48EW, 48EY024-068, 48AW, 48AY020-060 See below for building pressure to signal level

Power Exhaust — The optional non-modulating power exhaust (CV only) is a two-stage design where the operation of the exhaust fans is linked to economizer position. When the supply fan is running and the economizer is 25% open, the base control board closes contacts, activating 2 (48AJ,AK,AW, AY020-050 and 48EJ,EK,EW,EY024-048) or 3 (48AJ,AK, AW,AY060 and 48EJ,EK,EW,EY054-068) exhaust fans. When the economizer position reaches 75% open, the base module activates the other 2 (48AJ,AK,AW,AY020-050 and 48EJ,EK,EW,EY024-048) or 3 (48AJ,AK,AW,AY060 and 48EJ,EK,EW,EY054-068) exhaust fans. The fans will turn off when the economizer closes below the same points. The econ- omizer position set points that trigger the exhaust fans can be modified, but only through use of the Service Tool, Comfort- WORKS®, or Building Supervisor software. If single-stage operation is desired, adjust the economizer set points to identi- cal values at the desired point to activate all exhaust fans.

The optional modulating power exhaust (VAV standard, CV optional) is controlled by a modular electronic sequencer sys- tem. This system consists of a model R353 signal input module and 4 model S353 staging modules (for 48AJ,AK,AW,AY060 and 48EJ,EK,EW,EY054-068, 6 model S353 staging mod- ules). The signal input module receives a 0 to 10 vdc signal from the building pressure transducer, which is mounted adja- cent to the supply static transducer behind the filter access pan- el. The modules are mounted just below the unit control board. The left module is the R353, and the 4 or 6 modules on the right are S353 modules for stages 1 through 4 or 6. On the unit wiring label, the R353 is designated PESC, and the S353 modules are designated PES1 through PES4 (PES6 for 48AJ,AK,AW,AY060 and 48EJ,EK,EW,EY054-068).

The building pressure transducer range is -0.5 to + 0.5 in. wg. It is powered by a 0 to 10 vdc signal. A factory-installed hose at the ‘‘Lo’’ connection leads to atmosphere, and a field- supplied hose must be connected to the ‘‘Hi’’ connection and led into the building to a point where building pressure is to be controlled. There is a plug button in the bulkhead just above the transducers, for use in leading the hoses into the building via the return air ductwork.

There are 3 adjustments at the R353 module, all of which have been factory set. In the center of the circuit board is a set of 4 pins with a jumper, labeled J2. This determines the mode of operation. The bottom two pins must be jumpered for direct operation. Direct operation means that the staging modules are activated in sequence as the input signal increases.

At the upper right corner of the board is a set of 5 pins and jumper, which determines the time constant for the control. The time constant is the delay in response built into the con- trols. The jumper should be on the middle or bottom two pins, for the maximum time constant. The delay can be decreased, if desired, by moving the jumper progressively upward, always jumpering adjacent pins.

At the lower left corner of the board below the terminal strip is a resistor marked R27. This must be removed in order to ob- tain the 0 to 10 vdc signal output. There will not be a resistor on a factory-supplied module, but a resistor may be present on a replacement module and must be removed.

The R353 module has a terminal block with 7 connections available for wiring. The 2 right-hand terminals are for the 24 vac and common connections. The next 2 terminals are for the 0 to 10 vdc signal. Consult the wiring label for wire identi- fication if replacing the module. The 3 left-hand terminals are not used for this application.

The S353 module has an LED (light-emitting diode), a set of 4 jumper pins, and 2 potentiometers. The LED will light whenever the module is activated, providing a visual indication of the number of exhaust fans running. The jumper pins are ar- ranged in a square format. Two jumpers are used to determine

the mode of operation (direct or reverse). The 2 jumpers must be arranged horizontally for direct action (factory set).

At the top of the module are two potentiometers. The left potentiometer adjusts the offset. The right potentiometer ad- justs the differential. The potentiometers are factory set for a nominal 0 in. wg building pressure.

The offset set point is defined as the point at which a mod- ule turns off a fan, and is measured in terms of percent of the input signal. For control purposes, 0 offset is at an arbitrary ‘‘floor’’ which is established at 10% of the input signal, or 1 vdc. In this example, the first stage will turn off at 30% (3 vdc), and the offset potentiometer will be set at 20%. The second stage will turn off at 50% signal (5 vdc), and the offset potentiometer will be set at 40%. The fourth stage is at the maximum 75% offset, which equates to 85% signal or 8.5 vdc. The offset potentiometer is calibrated in 10% increments.

See below for building pressure to signal level.

BUILDING PRESSURE	SIGNAL LEVEL
(in. wg)	(vdc)
-0.50	2
-0.25	4
0.00	6
0.25	8
0.50	10

If the building pressure is controlled at 0 in. wg, offset of the first stage should be set at 50%, which equates to 60% of the input signal, or 6 vdc. The other stages can then be set as de- sired between 50% and 75%.

The default offset set points for modulating power exhaust are shown in Tables 16A and 16B.

The differential set point is the difference between the turn off point and the turn on point for each module. It also is cali- brated in terms of percent of input signal, and has a range of 1% to 7%. The differential potentiometer is calibrated in 1% increments, and is factory set at approximately 3%. It is recom- mended to leave the set point at 3%, to minimize cycling of the fans.

The offset and differential potentiometers have been factory set for atmospheric pressure. Do not change these settings until there is some experience with the building. In most cases the factory settings will be satisfactory. However, if the building pressure is not being maintained as desired, then some minor adjusting on a trial and error basis can be made.

Direct Digital Controls DIP Switch Configura- tion — The Direct Digital Control (DDC) board must be configured for each application. The DDC board is configured through the DIP (Dual In-Line Package) switches located on the board. There are 8 DIP switches which configure 8 differ- ent applications of the DDC. See Table 17. DIP switch 1 is on the left of the block. DIP switch 8 is on the right of the block. To open a DIP switch, push the switch up with suitable tool (small-blade screwdriver). To close a DIP switch, push the switch down. Factory settings are shown in Table 18.

The DIP switch configurations are as follows:

•DIP switch 1 configures the unit to operate as a VAV or CV unit

•DIP switch 2 configures the unit to use a space sensor (VAV units) or a thermostat (CV units)

•DIP switch 3 configures the DDC for use with an elec- tronic expansion board

•DIP switch 4 is used to field test the unit

•DIP switch 5 is used to enable occupied heating (VAV units) or specify the type of power exhaust (CV units)

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